Generally, in a wireless communication system, a number of wireless base stations have respective service areas to which the service of each base station is provided, and the service areas of the wireless base stations are overlapped each other.
In the IP (Internet protocol) network, there is an increasing demand for broadcasting communication applications, such as music or vide distributions. The studies of the protocols suitable for such applications in the IP network have been carried out. Hence, the wireless access communication system that supports the multicasting service is the important issue.
Multicasting is the ability of one network node (for example, a wireless base station) to send identical data to a number of end-point terminals (for example, wireless terminals). However, the service areas of wireless base stations are not necessarily appropriate for providing the wireless terminals with the multicasting services.
For example, it is often possible that multiple wireless base stations cover the same service area, in order to avoid network congestion.
FIG. 1 is a diagram for explaining a problem of a service area of a conventional wireless base station. In the example of FIG. 1, small service areas 3 through 6 are provided within a larger service area 1, and small service areas 7 through 9 are provided within a large service area 2.
FIG. 2 is an enlarged view of the large service area 1 of the conventional wireless base station in FIG. 1. As shown, in the large service area 1, a wireless base station B stands ready to provide its service. In the small service area 3, a wireless base station A stands ready to provide its service.
In the example of FIG. 2, a wireless terminal “a” exists in the service area 3, and a wireless terminal “b” exists in the service area 1. Each of the wireless base stations A and B provides the multicasting service. In the present example, the wireless terminal “a” can receive the multicasting service provided by the wireless base station A, and the wireless terminal “b” can receive the multicasting service provided by the wireless base station B.
When providing the multicasting service in a wireless access communication system in which the service areas of plural wireless base stations overlap each other, it is likely that the plural wireless base stations simultaneously send identical data to the overlapping service area. For the example of FIG. 2, in such a case, the wireless terminal “a” receives the multicasting service from the wireless base station A, and, at the same time, it receives the multicasting service from the wireless base station B. Namely, the wireless terminal “a” receives identical data from both the wireless base station A and the wireless base station B at the same time.
In the present example, it is sufficient for the wireless terminal “a” to receive the multicasting service from the wireless base station B only. It is not necessary that the wireless terminal “a” receive the multicasting service from the wireless base station A.
Hence, in the present example, the multicasting service provided to the wireless terminal “a” by the wireless base station A is inefficient. The radio resources are utilized inefficiently in the present example, and the efficiency of utilization of the radio resources is lowered.
Further, conventionally, when the services supported by the wireless base stations have to be changed in the individual base stations, the scheduling of the service changes of the wireless base stations is produced at another location other than the wireless base stations, and the service changes are effected at the respective base stations. Such conventional method requires high cost from the standpoint of maintenance and operation.
In order to eliminate the above-mentioned problems, one object of the present invention is to make efficient use of the radio resources and lower the maintenance and operation cost.
Further, when the access communication network is based on the IP network, the IGMP (Internet Group Management Protocol) can be used as the multicasting protocol. According to the IGMP protocol, it is determined whether the router sends the multicasting messages to the sub-network, in order to avoid the network congestion. When the access communication system is connected to the IP network that supports the IGMP protocol, it is preferred that the system employs the access control flow that is compatible with the IGMP protocol.
According to the IGMP protocol, in order to prevent the sending of unnecessary data to the sub-network, the multicasting is not performed for the packets having a group address that is not related to the sub-network. In addition, for the wireless access system that supports the multicasting, the sending of unnecessary data to the sub-network is avoided, and the radio resources are saved.
However, when two different routers A and B receive the packets having a same group address, the routers A and B perform the multicasting to send identical data to the terminals of the related group within the respective service areas thereof
In a wireless access communication system in which the service areas of plural wireless base stations overlap each other and some wireless terminal can simultaneously receive the multicasting services from the plural wireless base stations, it is likely that the wireless terminal is connected to the wireless base station that provides the highest level of communication quality for the wireless terminal.
FIG. 3 is a diagram for explaining another problem of a service area of a conventional wireless base station. As shown, reference numeral 1 denotes the service area of the wireless base station A, and reference numeral 2 denotes the service area of the wireless base station B.
As indicated in (A) in FIG. 3, the wireless terminal “a” is connected to the wireless base station A, and the wireless terminal “b” can be connected to both the wireless base station A and the wireless base station B. However, the wireless terminal “b” is located at the place that is nearer to the wireless base station B than the wireless base station A. As the wireless base station B provides a higher level of communication quality for the wireless terminal “b”, the wireless terminal “b” is connected to the wireless base station B and receives the service from the wireless base station B.
As indicated in (B) in FIG. 3, when the service area 4 of the wireless base station A is provided within the service area 3 of the wireless base station B, the wireless terminal “a” can be connected to both the wireless base station A and the wireless base station B. In the example of FIG. 3(B), the wireless base station A provides a higher level of communication quality for the wireless terminal “a” than the wireless base station B, and the wireless terminal “a” is connected to the wireless base station A and receives the service from the wireless base station A.
However, conventionally, in the example of FIG. 3(A), the wireless terminal “a” is connected to the wireless base station A according to the communication quality level, even when the wireless terminals “a” and “b” belong to the same IGMP group (group G1) and receive identical data. The wireless base station A sends to the wireless terminal “a” the identical data that is the same as that is sent to the wireless terminal “b”.
If the connection of the wireless terminal “b” and the wireless base station B is switched to the connection of the wireless terminal “b” and the wireless base station A when the wireless terminal “b” is the only terminal that belongs to the group G1 and exists in the service area 2 of the wireless base station B, the wireless base station B stops providing the multicasting service to the wireless terminal “b”. The radio resources needed for the wireless base station B to transmit other services to the group G1 terminals can be saved because of the disconnection of the wireless terminal “b” from the wireless base station B.
Further, in the example of FIG. 3(B), the wireless terminal “a” exists in the service area 3 of the wireless base station B, and the wireless terminal “a” can communicate with the wireless base station B as well. If the connection of the wireless terminal “a” and the wireless base station A is switched to the connection of the wireless terminal “a” and the wireless base station B, the radio resources needed for the wireless base station A can be saved.
In a conventional IGMP network, it is likely that, when different wireless base stations provide the multicasting service for the wireless terminals which belong to the same IGMP group and exist in the overlapping service area, the wireless base stations send identical data to the wireless terminals at the same time. The radio resources are used unnecessarily in such a situation, and the utilization of the radio resources is lowered.
In order to eliminate the above-mentioned problems, another object of the present invention is to reduce the number of the wireless base stations that send identical data to the wireless terminals and increase the efficiency of utilization of the radio resources.